US20050234553A1

US20050234553A1 - Intervertebral disc replacement prothesis

Info

Publication number: US20050234553A1
Application number: US11/106,358
Authority: US
Inventors: Jeffrey Gordon
Original assignee: Vanderbilt University
Current assignee: Vanderbilt University
Priority date: 1999-05-17
Filing date: 2005-04-14
Publication date: 2005-10-20

Abstract

An intervertebral disc prosthesis for placement between a first vertebra and a second vertebra adjacent to the first vertebra. In one embodiment, the intervertebral disc prosthesis includes a resilient member, a first support member and a second support member. The resilient member has an axis and a thickness that aries at least in one direction perpendicular to the axis. The first support member and the second support member are received in the resilient member that is arranged, in use, to be secured to the first vertebra and the second vertebra, respectively. The intervertebral disc prosthesis can generate a coupled motion in more than one possible direction responsive to a possible movement of at least one of the first vertebra and the second vertebra, among the resilient member, the first support member and the second support member.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a continuation-in-part of U.S. patent application Ser. No. 10/903,578, filed Jul. 30, 2004, entitled “INTERVERTEBRAL DISC REPLACEMENT PROSTHESIS,” by Jeffrey D. Gordon and John K. Song, which is a continuation-in-part of U.S. patent application Ser. No. 10/235,117, filed Sep. 5, 2002, entitled “INTERVERTEBRAL DISC REPLACEMENT PROSTHESIS,” by Jeffrey D. Gordon, which is a continuation-in-part of and claims benefit of U.S. patent application Ser. No. 09/572,057, filed May 17, 2000, now issued as U.S. Pat. No. 6,579,321, entitled “INTERVERTEBRAL DISC REPLACEMENT PROSTHESIS,” by Jeffrey D. Gordon and John M. Dawson, and which itself claims the benefit, pursuant to 35 U.S.C. §119(e), of provisional U.S. patent application Ser. No. 60/134,500, filed May 17, 1999, entitled “INTERVERTEBRAL DISC REPLACEMENT PROSTHESIS,” by Jeffrey D. Gordon, the contents of which are incorporated herein in their entireties by reference, respectively.

FIELD OF THE INVENTION

The present invention generally relates to a device for treatment of spine disorders, and in particular to the utilization of an intervertebral disc prosthesis to perform one or more functions of an intervertebral disc between an adjacent pair of vertebrae.

BACKGROUND OF THE INVENTION

Degenerative disc disease is a common condition of the intervertebral disc of the spine characterized by disc height collapse with or without disc herniation, osteophyte formation, foramenal stenosis, facet hypertrophy, synovial cyst, and other symptoms. Any or a combination of these findings can lead to pain or neurological deficit. Many of the symptoms of degenerative disc disease may be alleviated by decompression of the neural structures and immobilization of the involved spinal segments. Immobilization is typically achieved in the long term by removal of the disc and placement of bone graft. Temporary immobilization to encourage incorporation of the bone graft can be achieved with placement of rigid hardware such as screws and rods.
While immobilization and a successful fusion may relieve the pain associated with nerve impingement, the long-term consequences of eliminating the motion of the intervertebral disc show a tendency toward increased risk of failure of the adjacent discs. The lack of motion at the fusion site places increased biomechanical demands on the adjacent discs causing them to degenerate prematurely.
Replacement prostheses have been suggested for degenerative disc disease to allow motion at the operative disc level. Several types of artificial intervertebral discs for replacing a part or all of a removed disc have been developed, such as, ball and socket discs, and mechanical spring discs. However, these devices are devoid of stiffness and stability and rely on the remaining spinal elements, such as the ligaments, muscles and remaining intervertebral disc tissue, namely the annulus fibrosis, for stability. For example, U.S. Pat. No. 5,556,431 to Buttner-Janz, U.S. Pat. No. 5,507,846 to Bullivant and U.S. Pat. No. 5,888,226 to Rogozinski, all of which are incorporated herein by reference, disclosed prostheses that comprise ball and socket type joints. The ball and socket disc prostheses typically incorporate two plate members having cooperating inner ball and socket portions that permit articulating motion of the members during movement of the spine. These inventions rely on stretching the annulus fibrosis to put the prosthesis into compression to gain stiffness. There is a risk of altering the spine's biomechanics by increasing the disc height past the normal range and/or a risk of damage to the annulus fibrosis. If the disc space is not stretched enough an unstable spinal segment could result, possibly leading to pain and further injury. In addition, this low stiffness places detrimentally high loads on supporting ligaments and muscles, particularly during movement involving torsional rotation of the spine. Dislocation and wear are other concerns with this disc type. Implantation entails insertion of several separate pieces that must be properly aligned during surgery. The surgery is often performed with a minimal incision offering limited access to the insertion site. Perfect alignment after insertion could be difficult.
Mechanical spring discs usually incorporate one or more coiled springs disposed between metal endplates. The coiled springs preferably define a cumulative spring constant sufficient to maintain the spaced arrangement of the adjacent vertebrae and to allow normal movement of the vertebrae during flexion and extension of the spring in any direction. Disadvantages of the mechanical spring disc types include attachment of the coiled springs to the metal end plates and associated wear at the attachment points. Examples of mechanical spring discs are disclosed in U.S. Pat. No. 5,458,642 to Beer et al. and U.S. Pat. No. 4,309,777 to Patil.
Other prostheses have been suggested, for examples, see U.S. Pat. No. 6,136,031 and U.S. Pat. No. 6,296,664 to Middleton, U.S. Pat. No. 5,320,644 to Baumgartner, U.S. Pat. No. 5,827,328 to Buttermann and U.S. Pat. No. 5,676,702 to Ratron, all of which are incorporated herein by reference. These disc prostheses have their own inherent stiffness, but may not take into account that axial loads placed on the spine during activity are generally much larger than bending loads. Therefore, these prostheses would either bottom out under axial loads and offer no response to bending loads, or be stiff enough to support the axial loads and thereby too stiff to flex under bending loads.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to an intervertebral disc prosthesis for placement between a first vertebra and a second vertebra adjacent to the first vertebra. In one embodiment, the intervertebral disc prosthesis includes a resilient member that is arranged, in use, to be secured to the first vertebra and the second vertebra, respectively. The resilient member has a first end portion, a second end portion, and a body portion that define a cavity therebetween the first end portion and the second end portion with an axis, Z.
The body portion of the resilient member has a thickness that varies at least in one direction perpendicular to the Z axis. Furthermore, the body portion of the resilient member includes at least one slit formed therein. The at least one slit has at least one round around the axis Z of the resilient member with a first end and a second end. The at least one slit also has an axis approximately coincident with the axis Z of the resilient member. A thickness of the at least one slit may be either substantially constant or variable along the at least one slit. In one embodiment, the at least one slit is substantially in the form of at least one helical cut.
The first end portion of the resilient member includes an end body that substantially closes the cavity at the first end portion, where the end body has a first planer surface and an opposite, second planer surface. The first end portion of the resilient member also includes a substantially circular edge portion and a flange radially outwardly extending from the substantially circular edge portion of the first end portion. The second end portion of the resilient member comprises a substantially circular edge portion and a flange radially outwardly extending from the substantially circular edge portion of the second end portion. The first end portion and the second end portion of the resilient member define an angle, θ, therebetween.
Furthermore, the intervertebral disc prosthesis includes a first support member and a second support member. In one embodiment, the first support member has a curved surface, a substantially planar surface, a body portion defined therebetween the curved surface and the substantially planar surface, and a flange radially outwardly extending from an edge portion of the substantially planar surface. The second support member has a substantially planar surface, a curved surface and a body portion defined therebetween the substantially planar surface and the curved surface. The curved surface of the second support member and the curved surface of the first support member are substantially complimentary to each other, where one of the curved surface of the second support member and the curved surface of the first support member comprises a convex surface, and the other comprises a concave surface that is complimentary to the convex surface.
Both of the first support member and the second support member are received in the cavity of the resilient member such that the substantially planar surface of the second support member cooperates with the substantially planar surface of the first end portion of the resilient member, and the curved surface of the second support member cooperates with the curved surface of the first support member, respectively, for generating a motion in more than one possible direction responsive to a possible movement of at least one of the first vertebra and the second vertebra. In use, the motion generated responsive to a possible movement of at least one of the first vertebra and the second vertebra possibly is a coupled motion among the resilient member, the first support member and the second support member and allows axial extension, axial compression, axial rotation and lateral bending for a wearer of the intervertebral disc prosthesis by deformation of the intervertebral disc prosthesis. In one embodiment, the first support member and the second support member communicate to act as a transferor of force load generated responsive to a possible movement of at least one of the first vertebra and the second vertebra. The flange of the first support member engages the substantially circular edge portion of the second end portion of the resilient member circumferentially such that the substantially planer surface of the first support member substantially closes the cavity substantially at the substantially circular edge portion of the second end portion of the resilient member.
Moreover the intervertebral disc prosthesis includes at least one engaging element protruding axially outwardly from the substantially circular edge portion to engage the first vertebra in use, where the at least one engaging element comprises a plurality of teeth. The intervertebral disc prosthesis also includes at least one engaging element protruding axially outwardly from the substantially circular edge portion to engage the second vertebra in use, where the at least one engaging element comprises a plurality of teeth.
In one embodiment, the resilient member, the first support member and the second support member are made from same or different materials that are bio-compatible and surgically implantable. The bio-compatible and surgically implantable materials comprise at least one of ceramic, metal, composite, or polymer materials.
Furthermore, the at least one of the resilient member, the first support member and the second support member has a wear reducing coating that comprises a titanium nitride material.
In another aspect, the present invention relates to an intervertebral disc prosthesis for placement between a first vertebra and a second vertebra adjacent to the first vertebra. In one embodiment, the intervertebral disc prosthesis includes a resilient member, a first support member and a second support member. The resilient member has a first end portion, a second end portion, and a body portion defining a cavity therebetween the first end portion and the second end portion with an axis, Z. The body portion of the resilient member has at least one slit formed therein. The at least one slit has at least one round around the axis Z of the resilient member. In one embodiment, the at least one slit is substantially in the form of a helical cut. The resilient member is arranged, in use, to be secured to the first vertebra and the second vertebra, respectively. The second end portion of the resilient member includes an end body that substantially closes the cavity at the second end portion, where the end body has a substantially planer surface and an opposite, curved surface. In one embodiment, the curved surface has a convex surface.
The first support member has a substantially planar surface, and an opposite, curved surface, and a body portion defined therebetween the substantially planar surface and the curved surface. The second support member has a first curved surface, an opposite, second curved surface, a body portion defined therebetween the first curved surface and the second curved surface, and a flange radially outwardly extending from an edge portion of the first curved surface. The first curved surface of the second support member comprises a convex surface. The second curved surface of the second support member and the curved surface of the first support member are substantially complimentary to each other, where one of the second curved surface of the second support member and the curved surface of the first support member comprises a convex surface, and the other comprises a concave surface that is complimentary to the convex surface. Both of the first support member and the second support member are received in the cavity of the resilient member such that the substantially planar surface of the first support member cooperates with the substantially planar surface of the second end portion of the resilient member, and the curved surface of the second support member cooperates with the curved surface of the first support member, respectively, for generating a motion in more than one possible direction responsive to a possible movement of at least one of the first vertebra and the second vertebra. The flange of the second support member engages with the resilient member circumferentially at the first end portion such that the first curved surface of the second support member substantially closes the cavity substantially at the first end portion of the resilient member. In one embodiment, the generated motion comprises one of an axial motion along the axis Z, a radial translating motion, a rotating motion around the axis Z, a rotating motion around an axis that is different from the axis Z, and any mixture thereof.
Furthermore, the intervertebral disc prosthesis includes at least one engaging element protruding axially outwardly from the first end portion to engage the first vertebra in use, where the at least one engaging element comprises a plurality of teeth. The intervertebral disc prosthesis also includes additional engaging means associated with the at least one engaging element to engage the first vertebra in use, where the additional engaging means comprises a tab member. Moreover, the intervertebral disc prosthesis includes at least one engaging element protruding axially outwardly from the second end portion to engage the second vertebra in use, where the at least one engaging element comprises a plurality of teeth. Additionally, the intervertebral disc prosthesis includes additional engaging means associated with the at least one engaging element to engage the second vertebra in use, where the additional engaging means comprises a tab member.
These and other aspects of the present invention will become apparent from the following description of the preferred embodiment taken in conjunction with the following drawings, although variations and modifications therein may be affected without departing from the spirit and scope of the novel concepts of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of an intervertebral disc prosthesis according to one embodiment of the present invention.
FIG. 2 shows a cross-sectional side view of the intervertebral disc prosthesis along line A-A of FIG. 1.
FIG. 3 shows an exploded view of the intervertebral disc prosthesis, as shown in FIGS. 1 and 2.
FIG. 4 schematically shows a method for finding an instantaneous axis of rotation of a vertebra in motion relative to a fixed point.
FIG. 5 shows a cross-sectional side view of a normal spinal motion segment.
FIG. 6 shows a cross-sectional side view of a spinal motion segment having an intervertebral disc prosthesis placed in an intervertebral disc space according to one embodiment of the present invention.
FIG. 7 shows a side view of an intervertebral disc prosthesis according to one embodiment of the present invention.
FIG. 8 shows a perspective view of the intervertebral disc prosthesis as shown in FIG. 7.
FIG. 9 shows a perspective view of an intervertebral disc prosthesis according to another embodiment of the present invention.
FIG. 10 shows a cross-sectional side view of an intervertebral disc prosthesis according to one embodiment of the present invention.
FIG. 11 shows a cross-sectional side view of an intervertebral disc prosthesis according to another embodiment of the present invention.
FIG. 12 shows a cross-sectional side view of an intervertebral disc prosthesis according to yet another embodiment of the present invention.
FIG. 13 shows a cross-sectional side view of an intervertebral disc prosthesis according to an alternative embodiment of the present invention.
FIG. 14 shows a cross-sectional side view of an intervertebral disc prosthesis according to one embodiment of the present invention.
FIG. 15 shows a cross-sectional side view of an intervertebral disc prosthesis according to another embodiment of the present invention.
FIG. 16 shows a cross-sectional side view of an intervertebral disc prosthesis, according to yet another embodiment of the present invention.
FIG. 17 shows a perspective view of an intervertebral disc prosthesis according to one embodiment of the present invention.
FIG. 18 shows a cross-sectional side view of the intervertebral disc prosthesis as shown in FIG. 17.
FIG. 19 shows a perspective view of an intervertebral disc prosthesis according to another embodiment of the present invention.
FIG. 20 shows a cross-sectional side view of the intervertebral disc prosthesis as shown in FIG. 19.
FIG. 21 shows a perspective view of an intervertebral disc prosthesis according to yet another embodiment of the present invention.
FIG. 22 shows a front side view of the intervertebral disc prosthesis as shown in FIG. 21.
FIG. 23 shows a cross-sectional side view of the intervertebral disc prosthesis along line D-D as shown in FIG. 22.
FIG. 24 shows a perspective view of an intervertebral disc prosthesis according to an alternative embodiment of the present invention.
FIG. 25 shows a side view of an intervertebral disc prosthesis according to one embodiment of the present invention.
FIG. 26 shows a cross-sectional side view of the intervertebral disc prosthesis along line A-A, as shown in FIG. 25.
FIG. 27 shows a perspective view of the intervertebral disc prosthesis as shown in FIGS. 25 and 26.
FIG. 28 shows a side view of an intervertebral disc prosthesis according to another embodiment of the present invention.
FIG. 29 shows a cross-sectional side view of the intervertebral disc prosthesis along line B-B, as shown in FIG. 28.
FIG. 30 shows a perspective view of the intervertebral disc prosthesis as shown in FIGS. 28 and 29.
FIG. 31 shows a side view of an intervertebral disc prosthesis according to an alternative embodiment of the present invention.
FIG. 32 shows a cross-sectional side view of the intervertebral disc prosthesis along line D-D, as shown in FIG. 31.
FIG. 33 shows a perspective view of the intervertebral disc prosthesis as shown in FIGS. 31 and 32.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is more particularly described in the following examples that are intended as illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. Various embodiments of the invention are now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
The description will be made as to the embodiments of the present invention in conjunction with the accompanying drawings 1-33. In accordance with the purposes of this invention, as embodied and broadly described herein, this invention, in one aspect, relates to an intervertebral disc prosthesis for placement between a first vertebra and a second vertebra adjacent to the first vertebra.
Referring in general to FIGS. 1-6, and in particular to FIGS. 1-3 first, an intervertebral disc prosthesis 50 in one embodiment has a resilient member 100 that is arranged, in use, to be secured to a first vertebra 200 and a second vertebra 202, respectively. The resilient member 100 includes a first end portion 100 a, a second end portion 100 b, and a body portion 100 c defining a cavity 105 therebetween the first end portion 100 a and the second end portion 100 b.
The first end portion 100 a of the resilient member 100 includes a substantially circular edge portion 100 a 1 and at least one engaging element protruding axially outwardly from the substantially circular edge portion 100 a 1 to engage the first vertebra 200.
The second end portion 100 b of the resilient member 100 has a first substantially planar surface 100 b 2, a second, opposite substantially planar surface 100 b 4, and a bottom portion 100 b 3 that is defined by the first substantially planar surface 100 b 2 and the second substantially planar surface 100 b 4. Furthermore, the second end portion 100 b of the resilient member 100 has a substantially circular edge portion 100 b 1 and at least one engaging element protruding axially outwardly from the substantially circular edge portion 100 b 1 to engage the second vertebra 202. The bottom portion 100 b 3 engages the substantially circular edge portion 100 b 1 of the second end portion 100 b of the resilient member 100 radially. The first substantially planar surface 100 b 2 substantially closes the cavity 105 of the resilient member 100 substantially at the substantially circular edge portion 100 b 1.
The body portion 100 c of the resilient member 100 has an axis 103 and a slit 101 formed therein the body portion 100 c. The slit 101 has at least one round around the axis 103. The slit 101 also has an axis 101 a approximately coincident with the axis 103 of the body portion 100 c. Additionally, the slit 101 has a first end and a second end, where each of the first end and the second end terminates in an opening as shown, for example, more clearly in FIG. 7. A thickness of the slit 101 can be either substantially constant or variable along the slit 101. The slit 101 in one embodiment is substantially in the form of at least one helical cut formed in the body portion 100 c. In another embodiment, the slit 101 is substantially in the form of a double helical cut formed in the body portion 100 c. Furthermore, the body potion 100 c of the resilient member 100 has at least one more slit formed therein in addition to the slit 101.
The resilient member 100 resembles a helical coil or spring such that it allows the intervertebral disc prosthesis 50 to react to bending loads by flexing. The geometry of the helical slit 101 can determine the stiffness of the resilient member 100 and therefore the stiffness of the intervertebral disc prosthesis 50. For example, to produce a more flexible implant the thickness of the helical slit 101 can be increased so that less material of the resilient member 100 remains. The number of rounds affects the stiffness of the resilient member 100 as well. The spring action of the resilient member 100 will allow rotation and will have an inherent torsional stiffness that is also affected by the geometry of the helical slit 101. The range of motion of the intervertebral disc prosthesis 50 is affected by the point at which the resilient member 100 bottoms out, that is, the point at which a bending load causes adjacent rounds to come into contact. The range of motion is affected by the space between the rounds, which is equivalent to the thickness of helical slit 101 multiplied by the number of rounds. Therefore, the helical slit 101 can be tailored to match the mechanical and kinematical characteristics of a normal disc at any level in the spine.
The intervertebral disc prosthesis 50 further includes a first support member 102 and a second support member 104. The first support member 102 has a curved surface 102 a, a substantially planar surface 102 b and a body portion 102 c defined therebetween the curved surface 102 a and the substantially planar surface 102 b. The second support member 104 has a substantially planar surface 104 a, a curved surface 104 b and a body portion 104 c defined therebetween the substantially planar surface 104 a and the curved surface 104 b. The curved surface 102 a of the first support member 102 and the curved surface 104 b of the second support member 104 are substantially complimentary to each other, wherein one of the curved surface 102 a of the first support member 102 and the curved surface 104 b of the second support member 104 has a convex surface, and the other has a concave surface that is complimentary to the convex surface. In one embodiment, the curved surface 102 a of the first support member 102 is a convex surface while the curved surface 104 b of the second support member is a concave surface that is substantially complementary to the convex surface 102 a of the first support member 102, as shown in FIG. 2.
Both of the first support member 102 and the second support member 104 of the intervertebral disc prosthesis 50 are received in the cavity 105 of the resilient member 100 such that the substantially planar surface 102 b of the first support member 102 cooperates with the first substantially planar surface 100 b 2 of the second end portion 100 b of the resilient member 100, and the curved surface 104 b of the second support member 104 cooperates with the curved surface 102 a of the first support member 102, respectively, for generating a motion in more than one possible direction responsive to a possible movement of at least one of the first vertebra 200 and the second vertebra 202. The body portion 104 c of the second support member 104 engages the substantially circular edge portion 100 a 1 of the first end portion 100 a of the resilient member 100 radially. The substantially planar surface 104 a of the second support member 104 substantially closes the cavity 105 substantially at the substantially circular edge portion 100 a 1. The first support member 104 may be rigidly attached to the resilient member 100 by press-fit, threads, retaining ring, pins, welding or some other means known to people skilled in the art.
As assembled according to the present invention, the intervertebral disc prosthesis 50 can generate a coupled motion in more than one direction responsive to a possible movement of at least one of the first vertebra 200 and the second vertebra 202, among the resilient member 100, the first support member 102 and the second support member 104. The coupled motion allows extension, flexion, axial rotation and lateral bending for a wearer of the intervertebral disc prosthesis 50 by deformation of the intervertebral disc prosthesis 50. Specifically, cooperation of the substantially planar surface 102 b of the first support member 102 with the first substantially planar surface 100 b 2 of the second end portion 100 b of the resilient member 100 may permit the first support member 102 to move translationally with respect to the resilient member 100. The ball-and-socket communication mechanism between the first support member 102 and the second support member 104 enables the second support member 104 to rotate with respect to the first support member 104 around three orthogonal axes including the axis 103. The resilient member 100 is itself capable of moving along the axis 103 and rotating (bending) around an additional axis that is perpendicular to the axis 103 and an axis that is perpendicular to both the axis 103 and the additional axis. Furthermore, The ball-and-socket communication mechanism between the first support member 102 and the second support member 104 provides support to the intervertebral disc prosthesis 50, which acts as a transferor of axial compression loads.
In use, as schematically shown in FIG. 6, the intervertebral disc prosthesis 50 is placed between the first vertebra 200 and the second vertebra 202 such that the substantially planar surface 104 a of the second support member 104 communicates with the first vertebra 200 and the second substantially planar surface 100 b 4 of the second end portion 100 b of the resilient member 100 communicates with the second vertebra 202, respectively. Attachment of the intervertebral disc prosthesis 50 to both the first vertebra 200 and the second vertebra 202 involves both immediate and long-term fixation. In one embodiment, immediate fixation can be achieved with a mechanical bone attachment means. For example, as shown in FIGS. 1-3, the at least one engaging element protruding axially outwardly from the substantially circular edge portion 100 a 1 of the first end portion 100 a of the resilient member 100 surfaces may include a plurality of teeth 108 a to engage the first vertebra 200. The at least one engaging element protruding axially outwardly from the substantially circular edge portion 100 b 1 of the second end portion 100 b of the resilient member 100 surfaces may include a plurality of teeth 108 b to engage the second vertebra 202. Additionally, the substantially planar surface 104 a of the second support member 104, the second substantially planar surface 100 b 4 the second end portion 100 b of the resilient member 100 including teeth 108 a and 108 b can be coated with a bone ingrowth inducing osteoconductive substance such as sintered beads or sintered wires or an osteoinductive coating such as hydroxyapatite for long-term fixation. Osteoinductive and osteoconductive coatings have been used extensively in joint replacement for many years and have been proven to be effective.
The resilient member 100, the first support member 102 and the second support member 104 can be made from same or different materials that are bio-compatible and surgically implantable, wherein the bio-compatible and surgically implantable materials include at least one of ceramic, metal, composite, or polymer materials. The preferred material for the resilient member 100 should possess high fatigue strength such as cobalt chrome alloy, titanium, titanium alloy, stainless steel, or the like. The material for the first support member 102 and the second support member 104 should possess excellent wear resistance and compressive strength. Ceramics, titanium, titanium alloy, stainless steel, cobalt chrome, alloy composites, or polymers should preferably be used for these elements. Alternatively, a biocompatible material with a wear reducing coating can be utilized. For example, a titanium nitride coating may be used on the supports or the resilient member. In one embodiment, at least one of the resilient member 100, the first support member 102 and the second support member 104 has a coating that includes a titanium nitride material.
The instantaneous axis of rotation (hereinafter “IAR”) is a parameter that characterizes how one body rotates with respect to another body (or a fixed point) in planar motion. Normal spinal motion can be characterized as planar (2-dimesional) for pure flexion-extension. FIG. 4 demonstrates a general method for determining the IAR of the motion of a body from two positions. For instance, a body (a vertebra) 210 is initially at POSITION 1 having two points A₁and B₁, after a motion, the body 210 is located at POSITION 2. Points A₁and B₁move to corresponding points A₂and B₂, respectively in the POSITION 2. As a result, a translation vector A₁-A₂of point A₁of the body 210 is directed from point A₁to point A₂and has a bisector 212 perpendicular to the translation vector A₁-A₂. A translation vector B₁-B₂of point B₁of the body 210 is directed from point B₁to point B₂and has a bisector 214 perpendicular to the translation vector B₁-B₂. Both the translation vector A₁-A₂and the translation vector B₁-B₂constitutes a plane of the motion. An axis at an intersection 213 of the bisectors 212 of the translation vector A₁-A₂and the bisectors 214 of the translation vectors B₁-B₂is the IAR of the motion that is perpendicular to the plane of the motion.
The intervertebral disc prosthesis 50 in one embodiment of the present invention may incorporate a mobile IAR. In one embodiment as shown in FIGS. 1-3, the curved surface 102 a of the first support member 102 can be a convex surface, and the curved surface 104 b of the second support member 104 correspondingly has a surface suitable for receiving and communicating with the convex surface of the first support member 102. The convex surface of the first support member 102 may vary. For instance, it may range from a partial hemisphere to a full hemisphere or it may be an elongated element with a rounded or partially rounded end. Motion at the interface between the first support member 102 and the second support member 104 has an IAR at the center of the radius of the bearing surface of the first support member 102. This embodiment, as shown in FIG. 2, also allows translation between the first support member 102 and the resilient member 100. The combination of rotation and translation allows a range of possible IARs.
Referring now to FIG. 5, a cross-sectional view of a motion segment including a first vertebra 200, an intervertebral disc (hereinafter “IVD”) 204 and a second vertebra 202 is shown. An IAR for the adjacent vertebrae 200 and 202 in the normal lumbar spine is located on and/or near the superior endplate of the second vertebra 202 of the motion segment, as shown in FIG. 5. FIG. 6 shows the same cross-section view of the motion segment as FIG. 5, but with replacement of the intervertebral disc 204 with an intervertebral disc prosthesis 50 of the present invention. In order to prevent unnatural loading of facet joints 206, the IAR of the motion segment for the adjacent vertebrae 200 and 202 must be maintained in the same area as the one without replacing the intervertebral disc 204, as shown in FIG. 5. The mobile LAR described above allows the IAR of the motion between the first vertebra 200 and the second vertebra 202 to be substantially maintained at the same position after implantation of the intervertebral disc prosthesis 50.
Referring to FIGS. 7 and 8, an intervertebral disc prosthesis 50 according to an alternative embodiment of the present invention includes a resilient member 150 with an axis 151. The resilient member 150 has a plurality of perimeter slits 152 cut therein, where the plurality of perimeter slits 152 is approximately horizontal, instead of a helical-type slit, as shown in FIGS. 1-3. Preferably, each of the plurality of perimeter slits 152 is substantially at a right angle relative to the axis 151 of the resilient member 150. The perimeter slits 152 are orientated such that at least one slit is opened and at least one slit is closed under an action of bending loads imposed at any plane through the axis 151 of the resilient member 150. In the embodiment as shown in FIGS. 7 and 8, the plurality of perimeter slits 152 includes three perimeter slits. Each of the plurality of perimeter slits 152 terminates in a hole or a perimeter opening 154, with a diameter that is larger than the thickness of the slit so as to reduce stress concentration. In one embodiment, the perimeter opening 154 is circular-shaped. The depth, thickness and number of the perimeter slits 152 as well as the size of perimeter opening 154 affect the stiffness of the intervertebral disc prosthesis 50. The thickness and number of the perimeter slits 152 affect the range of motion of the intervertebral disc prosthesis 50.
An intervertebral disc prosthesis can be made into a variety of shapes, as long as the spirit of the invention is not adversely affected. That is, the intervertebral disc prosthesis of the present invention may have a surface, such as, for example, the upper surface or the lower surface, which is flat, convex in shape or is otherwise shaped to fit the cavity of a vertebral endplate. Furthermore, from a top view, the intervertebral disc prosthesis may be of a variety of shapes, for instance, circular, kidney-shaped, or oval-shaped. FIG. 9 shows an alternative embodiment of an intervertebral disc prosthesis 51 including a resilient member 160 that is oval shaped. A plurality of teeth 168 protrudes axially outwardly from one end portion of the resilient member 160 for engaging one of the first vertebra 200 and the second vertebra 202. A support member 164 provides the flexibility for the intervertebral disc prosthesis 51 to generate a motion in more than one direction responsive to a possible movement of at least one of the first vertebra 200 and the second vertebra 202.
Referring now to FIGS. 10-16, an intervertebral disc prosthesis is shown according to other embodiments of the present invention. FIG. 10 shows a cross-sectional view of an intervertebral disc prosthesis 52 in one embodiment, which has a resilient member 100 with an axis 103, a first support member 205 and a second support member 104. The first support member 205 is a full hemisphere that has a symmetrical axis 205 d and is sized to fit into the resilient member 100. The second support member 104 includes a concave surface 104 b having a symmetrical axis 104 d and is substantially complementary to a convex surface 205 a of the full hemisphere of the first support member 205. As assembled, both of the symmetrical axis 205 d of the first support member 205 and the symmetrical axis 104 d of the concave surface 104 b of the second support member 104 are substantially coincident with the axis 103 of the resilient member 100. In the embodiment, a fixed IAR is located at the center 205 c of the radius of the full hemisphere of the first support member 205 that is on the axis 103 of the resilient member 100.
FIG. 11 shows a cross-sectional view of an alternative embodiment of an intervertebral disc prosthesis 54 of the present invention that has a resilient member 100 with an axis 103, a first support member 305 and a second support member 304. The first support member 305 is a partial hemisphere such that when the first support member 305 is received in the resilient member 100 the center 305 c of the radius of the partial hemisphere is displaced from the axis 103 of the resilient member 100. The second support member 304 is configured to communicate with the partial hemispherical of the first support member 305. In such embodiment, the IAR is located at 305 c, as shown in FIG. 10. The embodiment of the intervertebral disc prosthesis 54 of the present invention demonstrates that the IAR of an intervertebral disc prosthesis can be tailored to match the IAR of a healthy intervertebral disc simply by altering the radius of curvature and the center of the radius of curvature of a partial hemispherical, first support member 305.
FIG. 12 shows an angulated intervertebral disc prosthesis 56 with an angulated resilient member 400 and an augmented first support member 405 and an augmented second support member 404. In the embodiment of the intervertebral disc prosthesis 56, the resilient member 400 has a thickness varying continuously from a longest size at one side to a shortest size at an oppose side such that when the first support member 405 and the second support member 404 are received in the resilient member 400, a planar surface 404 a of the second support member 404 and a planar surface 405 b of the first support member 405 have a angle θ, where 0<θ<180°. The angle θ incorporated into the angulated intervertebral disc prosthesis 56 is meant to maintain a natural lordosis of the lumbar or cervical spine or a natural kyphosis of the thoracic spine. This angle could be matched to any lordosis or kyphosis of an intervertebral disc level being replaced.
FIG. 13 shows an alternative embodiment of an intervertebral disc prosthesis 58 of the present invention. The intervertebral disc prosthesis 58 includes a resilient member 100, a first support member 505, a second support member 104, and a lower seat member 510. The resilient member 100 has a cavity 105 and a bottom portion 100 b having an inner surface 102 b. The first support member 505, the second support member 104, and the lower seat member 510 are housed into the cavity 105 of the resilient member 100 such that the lower seat member 510 is placed between the first support member 505 and the inner surface 102 b of the bottom portion 100 b of the resilient member 100 for communicating with the first support member 510, and the second support member 104 communicates with the first support member 505 for generating a motion in more than one direction respective to a possible movement of at least one of the first vertebra 200 and the second vertebra 202. The resilient member 100 may be made of a metal material, the first support member 505 and second support member 104 may be made of a ceramic material having a predetermined rigidity, and the lower seat member 510 may also be made of the ceramic so that all elements experiencing sliding contact would gain the advantage of low wear ceramic on ceramic contact.
Another alternative embodiment of an intervertebral disc prosthesis 60 of the present invention is shown in FIG. 14. The intervertebral disc prosthesis 60 includes a resilient member 600 having a concave recess formed therein, and a first support member 605. The first support member 605 includes a first surface 605 a, a second surface 605 b and a flange 610 radially outwardly extending from an edge portion of the second surface 605 b, where the first surface 605 a is a convex surface that is complementary to and communicated with a surface of the concave recess of the resilient member 600. In this embodiment, a second support member is incorporated into the resilient member 600. The resilient member 600 may be rigidly attached to the flange 610 of the first support member 605 by welding, pins, retaining ring or some other means known to people skilled in the art.
An intervertebral disc prosthesis 62 having a resilient member 700, a first support member 705 and a second support member 704 is shown in FIG. 15 according to another embodiment of the present invention. The resilient member 700 includes a spring element that is a conventional helical spring made by forming a wire into a helix. The first support member 705 has a surface 705 b and a flange 710 radially outwardly extending from an edge portion of the surface 705 b. The second support member 704 has a surface 704 a and a flange 708 radially outwardly extending from an edge portion of the surface 704 a. The first support member 705 and the second support member 704 are made to communicate with each other and to communicate with the resilient member 700 for generating a motion in more than one direction respective to a possible movement of at least one of the first vertebra 200 and the second vertebra 202. The resilient member 700 may be rigidly attached to both the first support member 705 and the second support member 704.
FIG. 16 shows an intervertebral disc prosthesis 64 according to one embodiment of the present invention. The intervertebral disc prosthesis 64 includes a resilient member 800 and a upper disc support member 104. The resilient member 800 has a protuberance 805 that serves as a lower disc support member. The upper disc support member 104 is made to communicate with the protuberance 805 such that when assembled, the intervertebral disc prosthesis 64 enables o generate a motion in more than one direction respective to a possible movement of at least one of the first vertebra 200 and the second vertebra 202.
Referring now to FIGS. 17 and 18, an intervertebral disc prosthesis 918 according to an alternative embodiment of the present invention includes a resilient member 902, a first support member 924 and a second support member 922. The resilient member 902 has a first end portion 904, a second end portion 906, and a body portion 908 defining a cavity 905 therebetween the first end portion 904 and the second end portion 906 with an axis Z. The body portion 908 includes a bellows member made by welding, hydroforming or other means known to people skilled in the art. The second end portion 906 includes a bottom portion 910 that substantially closes the cavity 905, where the bottom portion 910 has a first surface 912 and a second, opposite surface 914.
The resilient member 902 is arranged, in use, to be secured to a first vertebra 200 and a second vertebra 202, respectively. In the embodiment, as shown in FIGS. 17 and 18, the first end portion 904 of the resilient member 902 has at least one engaging element protruding axially outwardly from the first end portion 904 to engage the first vertebra 200 in use, where the at least one engaging element has a plurality of teeth 926. The second end portion 906 of the resilient member 902 has at least one engaging element protruding axially outwardly from the second end portion 906 to engage the second vertebra 202 in use, where the at least one engaging element includes a plurality of teeth 928.
The first support member 924 has a first surface 924 a, a second surface 924 b and a body portion defined therebetween. In one embodiment, the first surface 924 a is a curved surface and the second surface 924 b is a substantially planar surface. The second support member 922 has a first surface 922 a, a second surface 922 b and a body portion defined therebetween. As formed, one of the first surface 922 a and the second surface 922 b of the second support member 922 is a curved surface, and the other is a substantially planar surface. The first surface 924 a of the first support member 924 and the second surface 922 b of the second support member 922 are complimentary to each other such that one of them is a convex surface, and the other will be a concave surface that is complimentary to the convex surface.
Both the first support member 924 and the second support member 922 are received in the cavity 905 of the resilient member 902 such that the second surface 924 b of the first support member 924 cooperates with the first surface 912 of the bottom portion 910 of the resilient member 902 and the second surface 922 b of the second support member 922 cooperates with the first surface 924 a of the first support member 924, for generating a motion in more than one possible direction responsive to a possible movement of at least one of the first vertebra 200 and the second vertebra 202. This configuration allows the intervertebral disc prosthesis 918 to move axially along the axis Z, translate radially, rotate around the axis Z, and rotate around an axis Z′ that is different, or apart, from the axis Z. As assembled, the second support member 922 may be rigidly attached to the resilient member 902 or attached with the ability to rotate with respect to the resilient member 902 about the axis Z of the resilient member 902. The attachment of the second support member 922 to the resilient member 902 substantially closes the cavity 905 at the first end portion 904 of the resilient member 902.
FIGS. 19 and 20 show another embodiment of intervertebral disc prosthesis 938 of the present invention, where the intervertebral disc prosthesis 938 includes a resilient member 940, a first support member 924, a second support member 942 and a plate 950. The resilient member 940 has a first end portion 944, a second end portion 946, and a body portion 948 defining a cavity 952 therebetween the first end portion 944 and the second end portion 946 with an axis Z. The body portion 948 includes a metal bellows member made by welding, hydroforming or other means. The plate 950 having a first surface 950 a and a second surface 950 b may be rigidly attached to the second end portion 946 of the resilient member 940 or attached with the ability to rotate with respect to the resilient member 940 about the axis Z of the resilient member 940. The attachment of the plate 950 to the resilient member 940 substantially closes the cavity 952 at the second end portion 946 of the resilient member 940.
The first support member 924 has a curved surface 924 a and a planar surface 924 b. The second support member 942 has a curved surface 942 b, a planar surface 942 a and a flange 942 d radially outwardly extending from an edge portion of the planar surface 942 a. In the example, as shown in FIGS. 19 and 20, the curved surface 924 a of the first support member 924 is a convex surface, while the curved surface 942 b of the second support member 942 is a concave surface that is complimentary to the convex surface 924 a.
Both the first support member 924 and the second support member 942 are received in the cavity 952 of the resilient member 940 such that the planar surface 924 b of the first support member 924 cooperates with the first surface 950 a of the plate 950 and the curved surface 942 b of the second support member 942 cooperates with the curved surface 924 a of the first support member 942, for generating a motion in more than one possible direction responsive to a possible movement of at least one of the first vertebra 200 and the second vertebra 202. As assembled, the flange 942 d of the second support member 942 may be rigidly attached to the resilient member 940 at the first end portion 944 or attached with the ability to rotate with respect to the resilient member 940 about the axis Z of the resilient member 940 such that the planar surface 942 a of the second support member 942 closes the cavity 952 at the first end portion 944 of the resilient member 940.
The resilient member 940 is arranged, in use, to be secured to a first vertebra 200 and a second vertebra 202, respectively. In the embodiment of the intervertebral disc prosthesis 938, as shown in FIGS. 19 and 20, the planar surface 942 a of the second support member 942 has at least one engaging element protruding axially outwardly from the planar surface 942 a to engage the first vertebra 200 in use, where the at least one engaging element has a plurality of teeth 956. The second surface 950 b of the plate 950 has at least one engaging element protruding axially outwardly from the second surface 950 b to engage the second vertebra 202 in use, where the at least one engaging element includes a plurality of teeth 958.
Referring now to FIGS. 21-23, an intervertebral disc prosthesis 960 in another embodiment has a resilient member 968, a first support member 976 and a second support member 962. The resilient member 968 has a first end portion 904, a second end portion 906, and a body portion 908 defining a cavity 978 therebetween the first end portion 904 and the second end portion 906 with an axis Z. The body portion 908 has a helical slit 964 cut therein so as to allow the intervertebral disc prosthesis 960 to bend about three orthogonal axes including the axis Z. The helical slit 964 has at least one round formed around the body portion 908. The first end portion 904 includes a flanged edge 904 a. The second end portion 906 includes a bottom portion 910 that substantially closes the cavity 978, where the bottom portion 910 has a flanged edge 910 a, a first surface 912 and a second, opposite surface 914.
The first support member 976 has a curved surface and a substantially planar surface and is sized such that when the first support member 976 is housed within the cavity 978 of the resilient member 968 by cooperating with the substantially planar surface of the first support member 976 with the first surface 912 of the bottom portion 910 of the second end portion 906 of the resilient member 968, the first support member 976 is able to translate along two orthogonal axes that are perpendicular to the axis Z with respect to the first surface 912 of the bottom portion 910.
The second support member 962 has a curved surface and a substantially planar surface. The curved surface of the second support member 962 is substantially complementary to the curved surface of the first support member 976 so as to articulate the second support member 962 for allowing rotation about three orthogonal axes including the axis Z when the second support member 962 is received in the cavity 978 of the resilient member 968 by cooperating the curved surface of the second support member 962 with the curved surface of the first support member 976. In the embodiment of the intervertebral disc prosthesis 960, as shown in FIG. 23, the curved surface of the first support member 976 is a convex surface, while the curved surface of the second support member 962 is a concave surface that is substantially complementary to the convex surface. By receiving the second support member 962, the cavity 978 of the resilient member 968 is closed by the substantially planar surface of the second support member 962. The attachment of the second support member 962 to the resilient member 968 may be either rigid or in a way that the second support member 962 has the ability to rotate with respect to the resilient member 968.
As assembled, the intervertebral disc prosthesis 960 is a single piece construction that can generate a motion responsive to a possible movement of one or both of the first vertebra 200 and the second vertebra 202. The motion is a coupled motion among the resilient member 968, the first support member 976 and the second support member 962 and allows extension, flexion, axial rotation and lateral bending for a wearer of the intervertebral disc prosthesis 960.
To secure the intervertebral disc prosthesis 960 to the first vertebra 200 and the second vertebra 202, respectively, the first end portion 904 of the resilient member 968 has at least one engaging element protruding axially outwardly from the flanged edge 904 a of the first end portion 904 to engage the first vertebra 200 in use, where the at least one engaging element has a plurality of teeth 966, as shown in FIGS. 21 and 22. Additionally, the first end portion 904 of the resilient member 968 has additional engaging means associated with the at least one engaging element to engage the first vertebra 200 in use, where the additional engaging means comprises a tab member 974 having at least one hole 972 for placement of a bone screw for additional attachment of the intervertebral disc prosthesis 960 to the first vertebra 200. The second end portion 906 of the resilient member 968 has at least one engaging element protruding axially outwardly from the flanged edge 906 a of the second end portion 906 to engage the second vertebra 202 in use, where the at least one engaging element includes a plurality of teeth 976. Furthermore, the second end portion 906 of the resilient member 968 includes additional engaging means associated with the at least one engaging element to engage the second vertebra 202 in use, wherein the additional engaging means comprises a tab member 974 having at least one hole 972 for placement of a bone screw for additional attachment of the intervertebral disc prosthesis 960 to the second vertebra 202.
Referring to FIG. 24, an intervertebral disc prosthesis 900 has a resilient member 910 having a first end portion 904, a second end portion 906, and a body portion 908 with an axis Z. The body portion 908 has a helical slit 902 cut therein so as to allow the intervertebral disc prosthesis 900 to bend about three orthogonal axes including the axis Z. The helical slit 902 has at least one round formed around the body portion 908. Alternatively, a plurality of helical slits may be cut into the body portion 908. The resilient member 910 can move in more than one possible direction responsive to a possible movement of at least one of the first vertebra 200 and the second vertebra 202.
In the embodiment of the intervertebral disc prosthesis 900, as shown in FIG. 24, the first end portion 904 of the resilient member 910 has at least one engaging element protruding axially outwardly from the first end portion 904 to engage the first vertebra 200 in use, where the at least one engaging element has a plurality of teeth 916. The second end portion 906 of the resilient member 910 has at least one engaging element protruding axially outwardly from the second end portion 906 to engage the second vertebra 202 in use, where the at least one engaging element includes a plurality of teeth 912.
Referring to FIGS. 25-27, an intervertebral disc prosthesis 1150 includes a resilient member 1100, a first support member 1120 and a second support member 1110. In one embodiment, the resilient member 1100 has a first end portion 1100 a, a second end portion 1100 b and a body portion 1100 c defining a cavity 1105 therebetween the first end portion 1100 a and the second end portion 1100 b with an axis, Z. The resilient member 1100 further has a thickness, h, defined therebetween a substantially circular edge portion 1100 a 1 of the first end portion 1100 a and a substantially circular edge portion 1100 b 1 of the second end portion 110Ob. The thickness h is non-uniform over the resilient member 1100. The thickness h varies in at least one direction perpendicular to the Z axis. In one embodiment, the thickness h varies continuously from one side to an opposite side of the resilient member 1100 as shown in FIG. 26. Alternatively, the resilient member can be formed such that the thickness h varies at least for a portion in a direction perpendicular to the Z axis from one side to an opposite side of the resilient member. The resilient member 1100 is arranged, in use, to be secured to the first vertebra 200 and the second vertebra 202, respectively.
The first end portion 1100 a of the resilient member 1100 includes an end body 1107 that substantially closes the cavity 1105 at the substantially circular edge portion 1100 a 1 of the first end portion 1100 a. In one embodiment, the end body 1107 has a first planer surface 1104 and an opposite, second planer surface 1108. The end body 1107 is formed such that the first planer surface 1104 and the second planer surface 1108 are not parallel to teach other. Alternatively, the end body can be formed with the first planar surface and the second planar surface are parallel to each other.
The body portion 1100 c of the resilient member 1100 has a slit 1106 formed therein. The slit 1106 has at least one round around the axis Z of the resilient member 1100 with a first end 1106 a and a second end (not shown). In one embodiment, the slit 1106 is substantially in the form of a helical cut formed in the body portion 1100 c of the resilient member 1100, as shown in FIGS. 25-27. The slit 1106 also has an axis 1109 approximately coincident with the axis Z of the resilient member 1100. In the embodiment shown FIGS. 25-27, the slit 1106 has a substantially constant thickness along the slit 1106. The slit 1106 may have a variable thickness along the slit 1106. The body portion 1100 c of the resilient member 1100 in one embodiment may have more than one slit formed therein.
As shown in FIG. 26, the first support member 1120 of the intervertebral disc prosthesis 1150 has a curved surface 1124, a substantially planar surface 1122, a body portion 1125 defined therebetween the curved surface 1124 and the substantially planar surface 1122, a flange 1126 radially outwardly extending from an edge portion of the substantially planar surface 1122, and a symmetrical axis, Z₁. The second support member 1110 of the intervertebral disc prosthesis 1150 has a substantially planar surface 1112, a curved surface 1114 and a body portion 1115 defined therebetween the substantially planar surface 1112 and the curved surface 1114. The curved surface 1114 of the second support member 1110 and the curved surface 1124 of the first support member 1120 are substantially complimentary to each other. In one embodiment, the curved surface 1114 of the second support member 1110 is concave, while the curved surface 1124 of the first support member 1120 is convex, which is complimentary to the surface 1114, as shown in FIG. 26. In another embodiment, the curved surface 1114 of the second support member 1110 is a convex, while the curved surface 1124 of the first support member 1120 is concave and complimentary to the curved surface 1114.
In one embodiment, the intervertebral disc prosthesis 1150 further has a plurality of teeth 1102 protruding axially outwardly from the substantially circular edge portion 1100 a 1 of the first end portion 1100 a of the resilient member 1100 for engaging the first vertebra 200, and a plurality of teeth 1103 protruding axially outwardly from the substantially circular edge portion 1100 b 1 of the second end portion 1100 b of the resilient member 1100 for engaging the second vertebra 202, respectively.
As assembled, both of the first support member 1120 and the second support member 1110 are received in the cavity 1105 of the resilient member 1100 such that the substantially planar surface 1112 of the second support member 1110 cooperates with the substantially planar surface 1108 of the first end portion 11 a of the resilient member 1100, and the curved surface 1114 of the second support member 1110 cooperates with the curved surface 1124 of the first support member 1120, respectively. In one embodiment, the first support member 1120 engages with the resilient member 1100 circumferencialy by attaching the flange 1126 of the first support member 1120 to the substantially circular edge portion 1100 b 1 of the second end portion 1100 b of the resilient member 1100. Accordingly, the substantially planer surface 1122 of the first support member 1120 substantially closes the cavity at the substantially circular edge portion 1100 b 1 of the second end portion 1100 b of the resilient member 1100. In this embodiment, the first planer surface 1104 of the first end portion 1100 a of the resilient member 1100 and the substantially planar surface 1122 of the first support member 1120 define an angle, θ, relative to each other, as shown in FIG. 26, where 0 <θ<180°, and the axis Z of the resilient member 1100 has an angle, β, relative to the axis Z₁of the first support member 1120, where 0<β<180°. The intervertebral disc prosthesis 1150 formed with the angle θ allows it to maintain a natural lordosis of the lumbar or cervical spine or a natural kyphosis of the thoracic spine after placement. This angle θ could be matched to any lordosis or kyphosis of an intervertebral disc level being replaced.
The intervertebral disc prosthesis 1150 is adapted for placement between a first vertebra 200 and a second vertebra 202 adjacent to the first vertebra 200 so as to generate a motion in more than one possible direction responsive to a possible movement of at least one of the first vertebra 200 and the second vertebra 202, where the first support member 1120 and the second support member 1110 communicate to act as a transferor of force load generated responsive to a possible movement of at least one of the first vertebra 200 and the second vertebra 202. The motion generated responsive to a possible movement of at least one of the first vertebra and the second vertebra may be a coupled motion among the resilient member 1100, the first support member 1120 and the second support member 1110 and allows extension, flexion, axial rotation and lateral bending for a wearer of the intervertebral disc prosthesis by deformation of the intervertebral disc prosthesis.
In another embodiment of the present invention shown in FIGS. 28-30, an intervertebral disc prosthesis 1250 includes a resilient member 1200. The resilient member 1200 has a first end portion 1200 a, a second end portion 1200 b and a body portion 1200 c defining a cavity 1205 therebetween the first end portion 1200 a and the second end portion 1200 b. The cavity 1205 is substantially closed at the second end portion 1200 b of the resilient member 1200. Furthermore, the resilient member 1200 has a slit 1206 formed therein the body portion 1200 c. The slit 1206 has at least one round around an axis, Z, of the resilient member 1200. In one embodiment, the slit 1206 is substantially in the form of a helical cut, as shown in FIGS. 28-30. The first end portion 1200 a of the resilient member 1200 has a flange 1233 radially outwardly extending from an edge portion of the first end portion 1200 a, and the second end portion 1200 a of the resilient member 1200 has a flange 1234 radially outwardly extending from an edge portion of the second end portion 1200 a.
As shown in FIG. 29, the intervertebral disc prosthesis 1250 also includes a first support member 1220 and a second support member 1210. The first support member 1220 includes a partial hemisphere 1225 having a symmetrical axis Z₁and is sized to fit into the resilient member 1200. The first support member 1220 further has a flange 1226 radially outwardly extending from an edge portion of the partial hemisphere 1225 such that when the first support member 1220 is received in the cavity 1205 of the resilient member 1200, the flange 1226 of the first support member 1220 substantially engages circumferentially the second end portion 1200 b of the resilient member 1200 so that a substantially planer surface 1222 of the first support member 1220 closes substantially the cavity 1205 at the second end portion 1200 b of the resilient member 1200. The second support member 1210 includes a concave surface 1214 having a symmetrical axis 1219 and is substantially complementary to a convex surface 1224 of the partial hemisphere 1225 of the first support member 1220. As assembled, the symmetrical axis 1219 of the second support member 1210 is substantially coincident with the axis Z of the resilient member 1200, while the symmetrical axis Z₁of the first support member 1220 is relative to the axis Z of the resilient member 1200 by an angle, β, and the substantially planer surface 1204 of the first end portion 1200 a of the resilient member 1200 and a substantially planar surface 1222 of the first support member 1220 define an angle, θ, relative to each other, where both β and θ are greater than zero and less than 180°, respectively, as shown in FIGS. 29.
Referring now to FIGS. 31-33, an intervertebral disc prosthesis 1350 includes a resilient member 1300, a second support member 1310 and a second support member 1310. In one embodiment, the resilient member 1300 has a first end portion 1300 a, a second end portion 1300 b, and a body portion 1300 c defining a cavity 1305 therebetween the first end portion 1300 a and the second end portion 1300 b, and a symmetrical axis, Z. The second end portion 1300 b includes an end body 1307 that substantially closes the cavity 1305 at the second end portion 1300 b, where the end body 1307 includes a substantially planer surface 1304 and an opposite, curved surface 1301. In one embodiment, the curved surface 1301 includes a convex surface. The body portion 1300 c of the resilient member 1300 has a slit 1306 formed therein substantially in the form of a helical cut so as to allow the intervertebral disc prosthesis 1350 to bend about three orthogonal axes including the axis Z. The slit 1306 has at least one round around the axis Z of the resilient member 1300. In one embodiment, the first end portion 1300 a of the resilient member 1300 has a flange 1333 radially outwardly extending from an edge portion of the first end portion 1300 a, and the second end portion 1300 a of the resilient member 1300 has a flange 1334 radially outwardly extending from an edge portion of the second end portion 1300 a.
In one embodiment, the first support member 1320 has a substantially planar surface 1324, a curved surface 1322, and a body portion 1325 defined therebetween the substantially planar surface 1324 and the curved surface 1322, and is sized such that when the first support member 1320 is housed within the cavity 1305 of the resilient member 1300 by cooperating with the substantially planar surface 1324 of the first support member 1300 with the first surface 1304 of the bottom portion 1307 of the second end portion 1300 b of the resilient member 1300, the first support member 1320 is able to translate along two orthogonal axes that are perpendicular to the axis Z with respect to the first surface 1304 of the bottom portion 1307.
The second support member 1310 has a first curved surface 1312, a second curved surface 1314, and a flange 1316 radially outwardly extending from an edge portion of the first curved surface 1312. The first curved surface 1312 of the second support member 1310 includes a convex surface. The second curved surface 1314 of the second support member 1310 is substantially complementary to the curved surface 1322 of the first support member 1320 so as to articulate the second support member 1310 for allowing rotation about three orthogonal axes including the axis Z when the second support member 1310 is received in the cavity 1305 of the resilient member 1310 by cooperating the second curved surface 1314 of the second support member 1310 with the curved surface 1322 of the first support member 1320. In the embodiment shown in FIG. 32, the curved surface 1322 of the first support member 1320 is a convex surface, while the second curved surface 1314 of the second support member 1310 is a concave surface that is substantially complementary to the convex surface 1322. By receiving the second support member 1310, the cavity 1305 of the resilient member 1310 is closed by the flange 1316 of the second support member 1310 such that a symmetrical axis 1329 of the first support member 1320 and a symmetrical axis 1319 of the second support member 1310 are substantially coincident with the symmetrical axis Z of the resilient member 1300, and the first curved surface 1312 of the second support member 1310 is symmetrical to the curved surface 1301 of the second end portion 1300 b of the resilient member 1300. The attachment of the second support member 1310 to the resilient member 1300 may be either rigid or in a way that the second support member 1310 has the ability to rotate with respect to the resilient member 1300.
As assembled, the intervertebral disc prosthesis 1350 is a single piece construction that can generate a motion responsive to a possible movement of one or both of the first vertebra 200 and the second vertebra 202. The motion is a coupled motion among the resilient member 1300, the first support member 1320 and the second support member 1310 and allows extension, flexion, axial rotation and lateral bending for a wearer of the intervertebral disc prosthesis 1350.
To engage the intervertebral disc prosthesis 1350 with the first vertebra 200 and the second vertebra 202, respectively, the first end portion 1300 a of the resilient member 1300 has at least one engaging element protruding axially outwardly from the flanged edge 1333 of the first end portion 1300 a to engage the first vertebra 200 in use, where the at least one engaging element has a plurality of teeth 1302, as shown in FIGS. 31-33.
Additionally, the first end portion 1300 a of the resilient member 1300 has additional engaging means associated with the at least one engaging element to engage the first vertebra 200 in use, where the additional engaging means comprises a tab member 1332.
The second end portion 1300 b of the resilient member 1300 has at least one engaging element protruding axially outwardly from the flanged edge 1334 of the second end portion 1300 b to engage the second vertebra 202 in use, where the at least one engaging element includes a plurality of teeth 1303. Furthermore, the second end portion 1300 b of the resilient member 1300 includes additional engaging means associated with the at least one engaging element to engage the second vertebra 202 in use, wherein the additional engaging means comprises a tab member 1331. Additionally, the second support member 1310 has a plurality of recesses 1317 formed therein the first curved surface 1312.
In some embodiments, an intervertebral disc prosthesis of the present invention includes a resilient member, a first support member and a second support member that are made from same or different materials that are bio-compatible and surgically implantable. The bio-compatible and surgically implantable materials comprise at least one of ceramic, metal, composite, or polymer materials. The preferred material for the resilient member should possess high fatigue strength such as cobalt chrome alloy, titanium, titanium alloy, stainless steel, or the like. The material for the first support member and the second support member should possess excellent wear resistance and compressive strength. Ceramics, titanium, titanium alloy, stainless steel, cobalt chrome, composites, or polymers should preferably be used for these elements. Alternatively, a biocompatible material with a wear reducing coating could be used. For example, a wear reducing coating such as diamond-like coating may be used on the supports or the resilient member. In one embodiment, at least one of the resilient member, the first support member and the second support member has a coating that includes a diamond-like material.
An intervertebral disc prosthesis of the present invention may be inserted into the spine using standard medical procedures. For example, see, Benzel, Spine Surgery: Techniques, Complication Avoidance, and Management, 1999, particularly in Section 11, pages 142-192, the contents of which are incorporated herein by reference. Additionally, when inserting the intervertebral disc prostheses of the present invention, the intervertebral disc prosthesis may be inserted such that the first support member is superior to (from a top view) the second support member. In other words, the intervertebral disc prosthesis may be used in a way such that the second support member is on the bottom and the first support member is on top. In certain situations, the intervertebral disc prosthesis of the present invention may be used without the first support member, the second support member, or both of them.
The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching.
The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.

Claims

1. An intervertebral disc prosthesis for placement between a first vertebra and a second vertebra adjacent to the first vertebra, comprising:

a. a resilient member arranged, in use, to be secured to the first vertebra and the second vertebra, respectively, having a first end portion, a second end portion and a body portion defining a cavity therebetween the first end portion and the second end portion with an axis, Z, wherein the first end portion includes an end body that substantially closes the cavity at the first end portion, the end body having a first planer surface and an opposite, second planer surface, and wherein the first end portion and the second end portion define an angle, θ, therebetween;

b. a first support member having a curved surface, a substantially planar surface, and a body portion defined therebetween the curved surface and the substantially planar surface; and

c. a second support member having a substantially planar surface, a curved surface and a body portion defined therebetween the substantially planar surface and the curved surface,

wherein both of the first support member and the second support member are received in the cavity of the resilient member such that the substantially planar surface of the second support member cooperates with the substantially planar surface of the first end portion of the resilient member, and the curved surface of the second support member cooperates with the curved surface of the first support member, respectively, for generating a motion in more than one possible direction responsive to a possible movement of at least one of the first vertebra and the second vertebra.

2. The intervertebral disc prosthesis of claim 1, wherein the body portion of the resilient member has at least one slit formed therein.

3. The intervertebral disc prosthesis of claim 2, wherein the at least one slit has at least one round around the axis Z of the resilient member.

4. The intervertebral disc prosthesis of claim 3, wherein the at least one slit is substantially in the form of at least one helical cut.

5. The intervertebral disc prosthesis of claim 3, wherein the at least one slit has an axis approximately coincident with the axis Z of the resilient member.

6. The intervertebral disc prosthesis of claim 3, wherein the at least one slit has a first end and a second end.

7. The intervertebral disc prosthesis of claim 3, wherein the at least one slit has a thickness that can be either substantially constant or variable along the at least one slit.

8. The intervertebral disc prosthesis of claim 1, wherein the first end portion of the resilient member comprises a substantially circular edge portion.

9. The intervertebral disc prosthesis of claim 8, further comprising at least one engaging element protruding axially outwardly from the substantially circular edge portion to engage the first vertebra in use.

10. The intervertebral disc prosthesis of claim 9, wherein the at least one engaging element comprises a plurality of teeth.

11. The intervertebral disc prosthesis of claim 10, wherein the first end portion of the resilient member further comprises a flange radially outwardly extending from the substantially circular edge portion.

12. The intervertebral disc prosthesis of claim 1, wherein the second end portion of the resilient member comprises a substantially circular edge portion.

13. The intervertebral disc prosthesis of claim 12, further comprising at least one engaging element protruding axially outwardly from the substantially circular edge portion to engage the second vertebra in use.

14. The intervertebral disc prosthesis of claim 13, wherein the at least one engaging element comprises a plurality of teeth.

15. The intervertebral disc prosthesis of claim 14, wherein the second end portion of the resilient member further comprises a flange radially outwardly extending from the substantially circular edge portion.

16. The intervertebral disc prosthesis of claim 1, wherein the curved surface of the second support member and the curved surface of the first support member are substantially complimentary to each other.

17. The intervertebral disc prosthesis of claim 16, wherein one of the curved surface of the second support member and the curved surface of the first support member comprises a convex surface, and the other comprises a concave surface that is complimentary to the convex surface.

18. The intervertebral disc prosthesis of claim 1, wherein the first support member further comprises a flange radially outwardly extending from an edge portion of the substantially planar surface.

19. The intervertebral disc prosthesis of claim 18, wherein the flange of the first support member engages with the resilient member circumferencialy such that the substantially planar surface of the first support member substantially closes the cavity substantially at the second end portion of the resilient member.

20. The intervertebral disc prosthesis of claim 1, wherein the thickness of the body portion varies in at least one direction perpendicular to the Z axis.

21. The intervertebral disc prosthesis of claim 1, wherein in use the motion generated responsive to a possible movement of at least one of the first vertebra and the second vertebra is a coupled motion among the resilient member, the first support member and the second support member and allows axial extension, axial compression, axial rotation and lateral bending for a wearer of the intervertebral disc prosthesis by deformation of the intervertebral disc prosthesis.

22. The intervertebral disc prosthesis of claim 21, wherein the first support member and the second support member communicate to act as a transferor of force load generated responsive to a possible movement of at least one of the first vertebra and the second vertebra.

23. The intervertebral disc prosthesis of claim 1, wherein the resilient member, the first support member and the second support member are made from same or different materials that are bio-compatible and surgically implantable.

24. The intervertebral disc prosthesis of claim 23, wherein the bio-compatible and surgically implantable materials comprise at least one of ceramic, metal, composite, or polymer materials.

25. The intervertebral disc prosthesis of claim 1, wherein at least one of the resilient member, the first support member and the second support member has a coating that comprises a titanium nitride material.

26. An intervertebral disc prosthesis for placement between a first vertebra and a second vertebra adjacent to the first vertebra, comprising:

a. a resilient member arranged, in use, to be secured to the first vertebra and the second vertebra, respectively, having a first end portion, a second end portion, and a body portion defining a cavity therebetween the first end portion and the second end portion with an axis, Z, wherein the second end portion includes an end body that substantially closes the cavity at the second end portion, the end body having a substantially planer surface and an opposite, curved surface;

b. a first support member having a substantially planar surface, and an opposite, curved surface, and a body portion defined therebetween the substantially planar surface and the curved surface; and

c. a second support member having a first curved surface, an opposite, second curved surface, and a body portion defined therebetween the first curved surface and the second curved surface,

wherein both of the first support member and the second support member are received in the cavity of the resilient member such that the substantially planar surface of the first support member cooperates with the substantially planar surface of the second end portion of the resilient member, and the curved surface of the second support member cooperates with the curved surface of the first support member, respectively, for generating a motion in more than one possible direction responsive to a possible movement of at least one of the first vertebra and the second vertebra.

27. The intervertebral disc prosthesis of claim 26, wherein the body portion 1300 c of the resilient member has at least one slit formed therein.

28. The intervertebral disc prosthesis of claim 27, wherein the at least one slit has at least one round around the axis Z of the resilient member.

29. The intervertebral disc prosthesis of claim 28, wherein the at least one slit is substantially in the form of a helical cut.

30. The intervertebral disc prosthesis of claim 26, wherein the generated motion comprises one of an axial motion along the axis Z, a radial translating motion, a rotating motion around the axis Z, a rotating motion around an axis that is different from the axis Z, and any mixture thereof.

31. The intervertebral disc prosthesis of claim 26, wherein the second support member further comprises a flange radially outwardly extending from an edge portion of the first curved surface.

32. The intervertebral disc prosthesis of claim 31, wherein the second support member is engaged with the resilient member circumferencialy through the flange of the second support member to substantially close the cavity substantially at the first end portion of the resilient member.

33. The intervertebral disc prosthesis of claim 26, wherein the second curved surface of the second support member and the curved surface of the first support member are substantially complimentary to each other.

34. The intervertebral disc prosthesis of claim 33, wherein one of the second curved surface of the second support member and the curved surface of the first support member comprises a convex surface, and the other comprises a concave surface that is complimentary to the convex surface.

35. The intervertebral disc prosthesis of claim 26, further comprising at least one engaging element protruding axially outwardly from the first end portion to engage the first vertebra in use.

36. The intervertebral disc prosthesis of claim 35, wherein the at least one engaging element comprises a plurality of teeth.

37. The intervertebral disc prosthesis of claim 36, further comprising additional engaging means associated with the at least one engaging element to engage the first vertebra in use.

38. The intervertebral disc prosthesis of claim 37, wherein the additional engaging means comprises a tab member.

39. The intervertebral disc prosthesis of claim 26, further comprising at least one engaging element protruding axially outwardly from the second end portion to engage the second vertebra in use.

40. The intervertebral disc prosthesis of claim 39, wherein the at least one engaging element comprises a plurality of teeth.

41. The intervertebral disc prosthesis of claim 40, further comprising additional engaging means associated with the at least one engaging element to engage the second vertebra in use.

42. The intervertebral disc prosthesis of claim 41, wherein the additional engaging means comprises a tab member.

43. The intervertebral disc prosthesis of claim 26, wherein the curved surface of the second end portion of the resilient member comprises a convex surface.

44. The intervertebral disc prosthesis of claim 26, wherein the first curved surface of the second support member comprises a convex surface.